The papers on the oxidation kinetics are reviewed to clarify the rate-controlling steps and the micromechanisms of oxidative attack. In the first part of the report, the general oxidation behavior of c/c composites is presented and then the detailed discussion is given on the relation of the oxidation rate to total surface area, to gas flow rate, to partial pressure of oxidizing gases and to the mechanical stresses. Finally, the oxidation rate of c/c composites with antioxidation treatments is discussed.

View full abstract

Heat transfer coefficient for packed beds have been evaluated using different correlations available in the literature assuming same process parameters with respect to temperature of the gas, temperature of the solid, void fraction of the bed, etc. The values calculated vary depending upon the equation used. As such, when these equations are used in a model for heat transfer in a fixed bed, for the same conditions, different temperature profiles are obtained. Equations that give close values for the heat transfer coefficient give rise to similar temperature profiles in packed beds. Equations predicting relatively lower heat transfer coefficients used in a model for describing the induration of pellets in a pot grate gave closer results to experimentally observed bed temperatures.

View full abstract

The rolling contact fatigue life of bearing steel is improved with decreases in the oxide nonmetallic inclusions. The oxygen content of high carbon chromium bearing steel has been reduced to an average level of 5.8ppm. This is accomplished through the combined processes of an electric arc furnace, a ladle furnace, an R-H vacuum degassing vessel and a continuous caster.
The rolling contact fatigue life of high-carbon chromium bearing steel thus manufactured has accordingly doubled to tripled on the test of a thrust type machine if compared with the results of the conventional vacuum degassed, ingot cast steel.
The supply of extremely low oxygen steel to the caster has resulted in the elimination of such troubles as nozzle clogging. From the operational standpoint, it has been the main contributor to a record 10 000t of continuous cast high-carbon chromium bearing steel from one tundish-one nozzle without interruptions.
It has been demonstrated in the life tests that neither sulfur nor titanium has an influence on the life when the levels of these elements are held down to a minimum in the high-carbon chromium bearing steel. The life is further extended by the cold working inherent to cold pilgered tubes. The improvement has been found out in the tests to double to triple life of hot worked hollow tubes.

View full abstract

the course of operation of 70 l UHP furnace in Chita Plant, Daido Steel, solid carbon has been injected in order to facilitate the reduction of FeO in slag and to improve the energy saving and heating efficiency. In this paper, the effect of the injection method on the reduction rate of FeO in slag is discussed in relation to the quality and size of carbon powder injected, injection rate and nature of molten slag. Moreover the relation between the fundamental data of waste gas and the degree of slag reduction has been comfirmed. The results obtained are summarized as follows:
(1) Volatile matter in solid carbon gives a large influence on the reducing reaction. In the coke of higher content of volatile matter, the reduction is controlled by the chemical reaction, while in the coke o f lower content of volatile matter, the reduction is controlled by the transport of FeO in slag.
(2) The reduction rate depends on the basicity of molten slag. The reduction rate increases as the basicity of molten slag increases.
(3) Estimation of carbon content of molten steel for a rapid operation is found to be possible by the use of the fundamental data of waste gas.

View full abstract

Critical review of thermodynamics of deoxidation of molten iron by Cr, V, Al, Zr, and Ti has been made. Experimental [wt.% O] vs. [wt. % M] data in these systems have been used to estimate first and second order cross-interaction parameters (e^M_O, r^M_O) employing five different calculation models. It was found that r^M_O should be considered for best fit. On the basis of this exercise, a simple analytical equation relating [wt.% O] and [wt.% M] has been proposed and values of e^M_O, r^M_O recommended. Assessments have also been made of deoxidation constants (K). Values of K for the above systems have been proposed based on selected experimental data and thermodynamic estimates. [wt.% O] vs. [wt.% M] solubility curves for molten iron in equilibrium with oxide product calculated from the accepted values of thermodynamic parameters, have been presented.

View full abstract

A study was made on the effects of alloying elements such as Si, Mn, Cr, Ni and Mo on the rotating bending fatigue properties of carburized steels. At first, the effect of Si was studied using commonly used grades, JIS SCM420 and SNCM420. It was shown that the decrease in Si content remarkably reduced internal oxidation and resulted in higher fatigue strength. In order to clarify the effects of other alloying elements, fatigue tests were carried out on low Si steels where the Si contents were less than 0.15%. Internal oxidation was reduced and fatigue resistance was improved with increasing Ni and Mo contents and with decreasing Cr and Mn contents when keeping the core hardness constant. The 0.2%C-3%Ni-0.45%Mo steel showed the highest fatigue limit of 100kgf/mm². High Ni-high Mo-low Mn-low Cr steels are considered to exhibit superior fatigue resistance by supressing internal oxidation and by the greater fracture toughness of carburized case.

View full abstract

The structural characteristics and mechanical properties of 9Ni and 9NiMo steels are reviewed with special reference to the aspects vital for the development of optimum heat treatment procedures. In the 9Ni steel, even comparatively high cooling rates have been found to entail the formation of ferrite in the structure, which not only impairs the strength properties in the initial state of the steel, but also makes it more susceptible to brittle failure. In the 9NiMo steel, the same ferrite-induced degrading mechanism was observed in a much weaker form. Parallel analyses of the incubation period of the ferrite formation during isothermal holding of austenite at 600°C indicated that the predicted incubation period for 9Ni steel was in agreement with the experimental data. It was also discovered that in 9NiMo after long term holding at 600°C particles of graphite are present in some ferrite grains.

View full abstract

The Fe-C-S ternary phase diagram has been calculated on the basis of the thermodynamic analysis of the Fe-S and Fe-C binary systems and the Fe-C-S ternary melt. The Gibbs energy of individual phases has been approximated by the interstitial solution model, assuming both C and S to be interstitial atoms. The influence of ferromagnetism on the Gibbs energy o f ferrite has been also taken into account. The calculated results show that the remelting reaction occurs during the cooling process of Fe-C-S alloy. This was confirmed by scanning electron microscopy on the fractured surface of Fe-C-S (0.02wt%) alloy, quenched from various temperatures. The effect of S on the single phase region of austenite was also studied, and the changing rate of the solidus temperature was estimated to be -1400°C per 1wt% S.

View full abstract